Home Cultivation The Eleventh Plague: Hemp Russet Mites

The Eleventh Plague: Hemp Russet Mites

The Promised Land of Prohibition's End is in Sight, But First - a Visit From a Nearly Invisible Angel of Death

Photo Courtesy of: O'Shaughnessy's Online http://www.beyondthc.com/the-latest-plague-aculops-cannabicola/

At CannaBiz gatherings in Northern California and online across the Internet, panicked growers are asking: “Who ARE Those Guys?” as a seemingly undetectable and unstoppable plague strikes fear in the hearts of both indoor and outdoor horticulturists.

Similar to the Tomato Russet Mite (Aculops lycopersici), the Hemp Russet Mite (Aculops cannabicola) is so tiny that infestation often goes unnoticed until the damage is irreparable. I’ve personally never had to deal with these bugs, thank goodness, but I’ve gathered the best info I could find for you and sadly, it’s mostly bad news.

You’ll see exaggerated claims that these mites are so small you need 200X magnification to see them, but that’s just not true, a 14X Loupe is all you need. This is one reason why I have urged you in previous blogs to carry and use an inexpensive but highly effective LED Illuminated 30X Jeweler’s Loupe, or even a hand held mini-microscope on your daily inspections. For five bucks you can’t go wrong with this magnifier and no one is compensating me for promoting this, it is the same device which was standard issue for the Master Gardener training program I went through last year here in California.

Hemp Russet Mites begin feeding on lower leaves and eventually work their way to the top of the plant, including flowers. Early signs of distress include progressive curling and drying out with bronzing of leaves and stems bottom to top. This is often ignored as just a bit of water stress or nutrient deficiency. Those leaves are sucked out and done, yesterday’s dinner, that’s not where the mites are now. Go up a level and microscopically inspect both sides of a few leaves directly above the damaged, unhealthy looking lower foliage.

As with Spider Mites, the warmer and drier the weather, the faster Hemp Russet Mites reproduce. Predatory Mites should be introduced as a natural preventative if Hemp Russet Mites or Spider Mites are known to have been a problem in the past. Any infestation will quickly weaken, wither and ruin Cannabis. Insecticidal Soaps and Herbal Oils are a waste of time and money against Hemp Russet Mites. Prune away, quarantine and safely dispose of any early isolated infested material; don’t be shy about sacrificing a few leaves, Colas or even an entire plant for the sake of your remaining crop.

Outdoors, Sulfur Dust and Wettable Sulfur will kill Hemp Russet Mites during the vegetative growth phase and is safe so long as no oils such as Neem are used for a few weeks before and after the application. Sulfur is generally considered an Organic friendly substance, but don’t use it once you are flowering the crop. Indoors, use a Sulfur Burner, but remember that the fumes of burning Sulfur are quite hazardous to humans; safety first!

I’ve seen a few wacky sounding “home remedies” on the Internet for battling Hemp Russet Mites and I’ll share two of them with the caveat that these methods are hearsay to me and untested. One grower claims to have killed Hemp Russet Mites by enclosing the entire plant in a large plastic bag, filling the bag with pure Carbon Dioxide, and leaving it to suffocate the bugs for several hours. A second and even more dramatic home remedy I found was to plunge the entire plant into an ice water bath, I’m guessing for no more than a few seconds to a minute or two. Got a method that works for you? Please leave a comment below.

Indoors, exclusion is the best preventative. Quarantine new plants, disinfect tools, use HEPA filters on incoming air ducting; generally respect the cleanliness and integrity of your grow space like a medical clean room. Consider soil-less, hydroponic grow methods to reduce the chance of introducing Hemp Russet Mites.

If you have the proper permits, you can use Abamectin on tomatoes to kill Russet Mites but “Sorry Charlie”, this level of chemical warfare while okay on food is a major No-No for Cannabis most anywhere. In Oregon for instance there is a Guide List of what may be applied, and Abamectin is not on the list. You may have heard recently that a pesticide popular with Organic Cannabis growers, Guardian Mite Spray, whose label listed only natural organic active ingredients such as cinnamon oil, was ordered to cease all sales when a lab discovered Abamectin in the mixture. No wonder it worked so well against Hemp Russet Mites, how convenient, eh?

So wait a darned minute, if chemicals like Abamectin are fine to use on produce, why not Cannabis? Because it is “Medicine”! Remember how we got here? Personally I think what is needed is a two-tier system, a state by state and eventually a national standard for Organic Cannabis certification for producers that want to go the certified pesticide-free medical route, and then another more relaxed, food grade set of rules for those who want to grow, distribute and market into the not-medicine retail trade. I have a nagging suspicion that some politicians may see super strict pesticide residue level rules as a way to effectively re-impose Cannabis prohibition, just sayin’.

Then there is the hairball of soil or “sun-grown” based organic versus hydroponic pesticide-free. Many Organic folk insist (without peer reviewed University research level scientific proof) that soil-less growing can never be as potently healthful as soil based due to the absence of beneficial mycorrhizal fungi and therefore hydroponic grown plants must not be labeled “Organic”. So, to keep the Organic folk sleeping peacefully at night we’ll have to introduce a labeling system that differentiates between soil grown organic and pesticide-free hydroponic.

As the Cannabis growing business comes out from the shadows, let’s hope the big money interests don’t muscle out the little guys who paved the way. We need the financial community to step up and offer the protection of Crop Insurance and futures hedging instruments to help modern Marijuana farmers get through bad times. Ask any Iowa sodbuster about droughts, pestilence and international politics driven corn market price fluctuations and their impact on multi-generational family land legacies.

Disclaimer: Any advice and opinions offered about the cultivation of cannabis by Bruce N. Goren are his own and do not represent the University of California or the Master Gardener Program.


  1. The drive to profit money is the problem, we should be farming small scale farms, which will have much more diversity and yield. Our goals should not to be to make a million of this a billion of that to end up with a bunch of numbers in our imagined accounting system. BUST through the veil! Our goals should better be to heal the planet then we heal each other and ourselves. The accounting system we call money has a fungus, its rigged by those who imagined it. Think of plan b. Because debt payments exceed new credit creation eventually in all debt based systems. Imagine money as a public resource, like water, everyone gets enough. How would that change how you do things?

    • To Miss Emily Peyton:
      First, mad props for comment as it TRULY came from the LIGHT of LOVE that you shine on so many everyday! Much love and respect to you and thank you for the LOVING FEELING it left with me.

      Second, to Marijuanatimes.org for having their heart ❤ built into their site lol as seeing the comment you left Miss Emily as the VERY FIRST ONE shows how they FEEL about the LOVE they share to all who visit.

      I’m not even a grower lol just an appreciative loving spirit following the vibrational energies from the LIGHT of LOVE we were created from so all those out there FEELING the positive change that LOVE energies are creating know I’m grateful for the LIGHT we are shining so positively brightly and spreading the LOVING FEELING!


      • A spray of 50% rubbing alcohol (70-91%) diluted with 50% water is very effective in killing russet mites. Also, before spraying your plants with this his solution, you should spray down each plant with a straight stream of water from a garden sprayer and particularly at the base of each leaf. This straight stream of water works wonders by knocking the mites off your plants and those left behind get the alcohol spray which kills those left behind. I have had success in getting my harvest in spite of the infestation. The pump sprayer cannon, should be used everyday while the alcohol spray should be used anytime you still are able to find a few mites lingering behind. Good luck!

  2. debating on spraying Avid, it’s August 1th so I know I can’t trim til Oct. 13th if I do. Last night I sprayed Kumulus df (I will not spray again as it is sulfer and they are starting to flower) Anyway I went up this morning plucked a couple of the bad leafs and there are hundreds of DEAD lil fuckers. Not sure about the eggs now, I think I’m going (August 16th) with a mixture of Dipel, Actinovate, Guard, Met 52 and yucca extract. I was also thinking maybe tetrasan on the 16th and push the other till the 20th or vice versa. Long story short Kumulus DF knocked them dead for now and that was overnight.

    I have 42 outdoor 8′ X 8′ plants ~ I prepared 100 gallons (2 cups Kumulus) (2 cups yucca extract) and ran it put of a tank through a booster pump with mist nozzle and drenched plants inside out upside down everywhere. (make sure you suit up as you will get mist all over you use a hazmat suit etc… they are $20 on ebay)

  3. To Emily Peyton – so correct I’m blown away at the amazing comment you left, If it would have stayed like that from the start we would be doing great,as a society / machine , any way I would like to personally qoute you in some art if u see this let me know

  4. But back on the mite im in calaveras , just ordered some predatory mites from arbico organics, they are great and have amazing info on russet mites on their webpage , ordered lady bugs for our tomatoes as well and they were so happy and alive it’s great! 9000 lady bugs for like 30 bucks

  5. I battled russet mites for a month. Thought I was gonna lose half my crap. Are used as azamax smite neem oil and a few IPMS but nothing worked. Then a friend told me about Amazing Doctor Zyme. And now I’m pest free.
    Amazing Doctor Zyme is the truth. It killed all bugs and helped the plants recover faster.

  6. Well written article. I’m glad we have people such as yourself to help us stay informed. However, one cannot consider oneself a master grower wo actually fighting russet and broad mites first hand. Another fight a true master must face, is the battle with certain pathogens. Fusarium oxysporom is another test to the master grower. Fusarium a generic label for bad fungus bacterium, plant pathogens. There are hundreds if nor thousands of them. Started in India and for the last two decades has reared havic on every plant that humans grow and is actually toxic to humans itself. The only way to know what you have is to collect samples of leaf, stem, roots and soil and either send to uc Davis if in ca. Or OSU if I. Oregon. Diagnosis of a plant pathologist is critical and in many cases free. Once you learn what you have you can decide what to do. Of course you can identify russet and broad mites and root afids w common microscope. But pathogens do the same destruction as these mites. You may have both. Don’t rely on the internet. Let the experts tell you what you have. Here is what I have learned. It all comes in on the soil or infected plants. Once infected plant comes in, your soil and every tool you have is infected. Air pots good. The more oxygen you soil has the better, but if you have a pathogen such as fusarium oxysporium, you mise well kill everything and start over. Soil must be baked at 220 or pressure treated. Best to get rid of soil and buy soil that has already been treated. If your outside this shit can live in your holes forever and survive through whatever. Let a pathologist tell you what you have. ….. Joel Sugar Mountain Cannabis Eugene Oregon.

    • Thanks Joel,
      This is yet another reason why we need to De-schedule Cannabis so the Land Grant Colleges can get to work studying challenges that growers like you face. The organisms which cause Fusarium Wilt have evolved to specialize in attacking certain plants and plant families. You have expressed anecdotal evidence that there is a Cannabis specific oxysporom! In the case of Tomatoes for instance, University research has developed some resistant strains through breeding programs. Some hothouse tomato growers graft susceptible cash crop heirlooms and novelty strains onto disease resistant root-stocks. I’ve been teaching grafting technique to propagators at a well-known Cannabis clone provider, this has great potential benefit for yield improvement and disease resistance down the road.

  7. In Mendocino we had a a russet mite problem and we used this mixture to keep them in check. Not sure it eliminated them, but we got the crop finished and it seemed to stop the problem. 1 cup of sugar, one asprin and 1 tsp maxi crop in a gallon of water sprayed on the plants. It worked well, but we want to make sure it does not come back this year. This was outdoors. Any idea how to treat the soil to kill them all before planting?

    • Laytonvillian,
      Have you tried the enzyme product that Woody Da Wookie mentioned in an earlier comment? Spraying the soil should kill off most of the eggs if it lives up to claims. You should also consider “baking” the soil by covering it with black plastic and letting the sun heat things up. Introduce predatory mites as soon as weather allows (Careful ! That enzyme product will probably also kill your beneficials ) and stay vigilant with daily inspections of the undersides of lower leaves.


  8. Familiar with the doctorzymes. I understand it works well. Just now seeing Russet mites. I disagree with the article in regards to spotting. under 10x they are invisible. under 100x I can see them. the russet Mites are most noticeable when the populations rise to a high enough level that they gather on the edges of new leaves. like tiny little pixels you can see the color they are due to the massive amounts of numbers. Swirski Mites are a good beneficial mite. I also use a liquid sulfur. Unlike the regular mites, russet mites can be found on both sides of the leaves. unless you thoroughly drench the plants nothing applied will be effective. dipping the whole plant when young is the most effective means I’ve found.

  9. I sprayed my outdoor plants with one foliar application of sulfur on 8/6 in Portland, Oregon. This was before they had any bloom or even began to stretch for that phase. I expect the strains I am growing (Chemdog, sour diesel, gorilla glue) to finish around the end of October or star of November here. Can anybody offer insight regarding the relative safety of consuming the flower? This is my personal medicine and I have been meticulous about my cultivation practices (living soil, dragonfly earth medicine teas, top dresses, bokashi). I am extremely nervous that I stand to risk my health at this point. Thanks.

  10. Food is also medicine!!! Also you can use abamectin forbid all these organic sprays “you shouldn’t use” just don’t spray flowers pre flowers or anywhere near a plant that might be flowering then or soon.. simple….

  11. Just discovered larvae, no actual mites yet. I am a week or two away from harvesting. Buds seem okay. Will this bud be safe to smoke? Will they contaminate my trimming room? Should I just discard everything?

  12. Obviously cleanliness and prevention. We have had success with suffoil. Used to spray floor pots and stem area if plants. Sometimes diluted with water to dunk clones being careful not to wet roots. Vaseline around the RI. Of your pots will stop the little bastards, you’ll see them get stuck and pile up sometimes by the thousands. Has worked for us.. beneficial predator bugs blah blah

  13. Seriously, try Circadian Sunrise. Essential oil-based pesticides do a great job of killing all types of mites, and Circadian Sunrise doesn’t strip the waxes from leaves like other essential oil-base products. Weekly applications will optimize plant health, whether or not you have mites. Treat have your plants starting from rooted clones or seedlings and you’ll see a big difference. Y

  14. I have been fighting these bugs for a few years now. 1) They always seem to come back. 2) almost none of the remedies I have found work including sulfur. I finally have found a remedy that seems to be working better than anything else I’ve tried. Here it is. Mix 50/50 91% isopropyl alcohol and RO or Distilled water in a spray bottle. DO NOT add any soap’s or other agents that could keep the formula from evaporating. Just mix the water and alcohol. Shake vigorously then spray the entire plants including both sides of the leaf and stem. Plus spray the stems and soil surface. Keep your plants out from under the lights until they dry completely. I take it a step further and spray down as much of the grow area as possible. Repeat every couple of days for about a week. Like I said this should kill off most of them but mine keep coming back and I believe that it’s someone growing and not killing them all.